High-wattage power meters are frequently used in industry to monitor various operational parameters of large electrical devices such as motors, lathes, pumps and the like. Such meters must be tested and calibrated periodically to insure their accuracy, not only at the time of manufacture but after installation. Typical calibration procedures call for electrically interconnecting the device under test with an actual load capable of operating the meter to its full scale which can be as high as several hundred thousand watts. Such test loads are often prohibitively large and expensive. For example, many typical industrial buildings have 220 volts at 100 amps three-phase service. In order to calibrate a 200 horsepower meter (equivalent to 149,200 watts) at full scale, more than 60 percent of the buildings total electrical service capacity would be required. Furthermore, this amount of power being dissipated by an actual load within such a building, would require 4.2 refrigeration tons of cooling to nullify the heat dissipated by the load.
An alternative calibration procedure, which is employed for larger power meters, requires the electrical interconnection of the meter under test with an actual source and load through calibrated reference shunts, current transformers, voltage transformers and the like. Although simulating a large load, such an arrangement still necessitates the dissipation of large amounts of power in the actual load. Additionally, the phase angle between the load voltage and current is not selectively variable. Finally, the tolerances of the shunts and transformers are compounded, thereby limiting the accuracy to which the meter may be calibrated.